1. Technical Field
The present invention relates to power control in general, and in particular to a method for providing power control on a computer system having a network device and a wakeup function.
2. Description of Related Art
There has been an increasing demand, from an environmental-oriented viewpoint, to reduce power that is required while a system, such as a computer, is being powered down, particularly when the standby power is being supplied from a power supply device such as an AC adapter. According to the criteria set for Eco Mark of Japan Environment Association, effective since 2000, the power during power-down should be 1 W or less for a system including an AC adapter and having no wakeup function, and should be 3 W or less for a system having a wakeup function.
A wakeup function is a function of starting up a remote computer by turning on a computer via a remote operation. With the wakeup function, a remote computer can be turned on by an instruction from a network on the basis of an operation at a remote location, instead of being turned on manually by an operator. WAKE-ON-LAN is an example thereof, and the function allows powered-downed computers to be collectively and centrally managed.
A computer has active logic that consumes power when implementing a wakeup function based on a communication even during power-down. As a result, a computer implementing a wakeup function requires more power during power-down, as compared with a computer having no wakeup function. In the case of WAKE-ON-LAN, one of the factors responsible for the power consumption at a wakeup time is a wakeup power source Vaux for an intended Ethernet adapter, which needs to be kept on in order to start a PC by recognizing a specific packet from a network.
One technique for reducing standby power during power-down is by using three types of control: a wakeup function set by a user; a device actually capable of implementing the wakeup function; and power supplied from an auxiliary power source only to the device that is capable of implementing the wakeup function.
Another technique allows a power supply circuit to generate a set of power sources, including a power source for a network controller, generally from DC power that is generated from AC power by an AC adaptor, but from a battery in the state where the AC power is down, and an EC/KBC controls the power supply circuit to turn off the network controller in the state where the AC power is down while the system is in a sleep or shutdown state.